Filter media including a filtration layer comprising synthetic fibers

ABSTRACT

Filter media comprising a filtration layer comprising synthetic fibers (e.g., pleatable backer layer) and related components, systems, and methods associated herewith are provided. In some embodiments, the filtration layer comprising synthetic fibers may be a non-woven web comprising a blend of coarse and fine diameter fibers. The filtration layer comprising synthetic fibers may be designed to have desirable performance properties without compromising certain mechanical properties, such as the pleatability of the media. In some embodiments, a filter media, described herein, may comprise the filtration layer comprising synthetic fibers and an efficiency layer. Filter media, as described herein, may be particularly well-suited for applications that involve filtering air, though the media may also be used in other applications.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/045,538 filed Feb. 17, 2016, which is incorporated herein byreference in its entirety.

FIELD OF INVENTION

The present embodiments relate generally to filter media including afiltration layer comprising synthetic fibers, and specifically, tofilter media having enhanced filtration properties.

BACKGROUND

Various filter media can be used to remove contamination in a number ofapplications. Filter media may be designed to have different performancecharacteristics, depending on their desired use. For example, relativelylower efficiency filter media may be used for heating, ventilating,refrigerating, air conditioning applications. For applications thatdemand different performance characteristics (e.g., very highefficiency), such as for clean rooms or biomedical applications, highefficiency particulate air (HEPA) or ultra-low penetration air (ULPA)filters may be used.

Filter media can be used to remove contamination in a variety ofapplications. In general, filter media include one or more fiber webs.The fiber web provides a porous structure that permits fluid (e.g., air)to flow through the web. Contaminant particles contained within thefluid may be trapped on the fiber web. Fiber web characteristics (e.g.,pore size, fiber dimensions, fiber composition, basis weight, amongstothers) affect filtration performance of the media. Although differenttypes of filter media are available, improvements are needed.

SUMMARY OF THE INVENTION

Filter media including a filtration layer comprising synthetic fibers(e.g., pleatable backer layer), and related components, systems, andmethods associated therewith are provided. The subject matter of thisapplication involves, in some cases, interrelated products, alternativesolutions to a particular problem, and/or a plurality of different usesof structures and compositions.

In one set of embodiments, filter media are provided. In one embodiment,a filter media comprises a non-woven web comprising first syntheticfibers having an average fiber diameter of greater than or equal toabout 15 microns, wherein the weight percentage of first syntheticfibers of all fibers in the non-woven web is greater than or equal toabout 40 wt. %; and second synthetic fibers having an average fiberdiameter of greater than or equal to about 0.5 microns and less thanabout 15 microns, wherein the weight percentage of second syntheticfibers of all fibers in the non-woven web is less than or equal to about50 wt. %, and wherein the surface average fiber diameter of thenon-woven web is greater than or equal to about 13 microns and less thanor equal to about 17 microns and is measured using the formula:

${{SAFD}\left\lbrack {{in}\mspace{14mu} {um}} \right\rbrack} = {4/\left( {{SSA}\mspace{14mu} {\rho \left\lbrack {{in}\frac{g}{{cm}3}} \right\rbrack}} \right)}$

wherein SSA is the BET surface of the filtration layer in m²/g and ρ isthe density of the layer in g/cm³. The filter media may also comprise anefficiency layer and the filter media has a dust holding capacity ofgreater than or equal to about 20 g/m².

In another embodiment, a filter media comprises a non-woven webcomprising first synthetic fibers having an average fiber diameter ofgreater than or equal to about 15 microns, wherein the weight percentageof first synthetic fibers of all fibers in the non-woven web is greaterthan or equal to about 40 wt. %; and second synthetic fibers having anaverage fiber diameter of greater than or equal to about 0.5 microns andless than about 15 microns, wherein the weight percentage of secondsynthetic fibers of all fibers in the non-woven web is less than orequal to about 50 wt. %, wherein the surface average fiber diameter ofthe non-woven web is greater than or equal to about 13 microns and lessthan or equal to about 17 microns and is measured using the formula:

${{SAFD}\left\lbrack {{in}\mspace{14mu} {um}} \right\rbrack} = {4/\left( {{SSA}\mspace{14mu} {\rho \left\lbrack {{in}\frac{g}{{cm}3}} \right\rbrack}} \right)}$

wherein SSA is the BET surface of the filtration layer in m²/g and ρ isthe density of the layer in g/cm³, and wherein the basis weight of thenon-woven web is less than or equal to about 110 g/m². The filter mediamay also comprise an efficiency layer.

In another set of embodiments, a wetlaid non-woven web is provided. Inone embodiment, a wetlaid non-woven web comprises first synthetic fibershaving an average fiber diameter of greater than or equal to about 15microns, wherein the weight percentage of first synthetic fibers of allfibers in the wetlaid non-woven web is greater than or equal to about 40wt. %; and second synthetic fibers having an average fiber diameter ofgreater than or equal to about 0.5 microns and less than about 15microns, wherein the weight percentage of second synthetic fibers of allfibers in the wetlaid non-woven web is less than or equal to about 50wt. %, and wherein the surface average fiber diameter of the wetlaidnon-woven web is greater than or equal to about 13 microns and less thanor equal to about 17 microns and is measured using the formula:

${{SAFD}\left\lbrack {{in}\mspace{14mu} {um}} \right\rbrack} = {4/\left( {{SSA}\mspace{14mu} {\rho \left\lbrack {{in}\frac{g}{{cm}3}} \right\rbrack}} \right)}$

wherein SSA is the BET surface of the filtration layer in m²/g and ρ isthe density of the layer in g/cm³.

In yet another set of embodiments, methods are provided. In oneembodiment, a method of manufacturing a non-woven web comprisesproviding first synthetic fibers having an average fiber diameter ofgreater than or equal to about 15 microns; providing second syntheticfibers having an average fiber diameter of greater than or equal toabout 0.5 microns and less than about 15 microns; and forming anon-woven web using a wetlaid process, wherein the weight percentage offirst synthetic fibers of all fibers in the non-woven web is greaterthan or equal to about 40 wt. %, the weight percentage of secondsynthetic fibers of all fibers in the non-woven web is less than orequal to about 50 wt. %, and the surface average fiber diameter of thenon-woven web is greater than or equal to about 13 microns and less thanor equal to about 17 microns and is measured using the formula:

${{SAFD}\left\lbrack {{in}\mspace{14mu} {um}} \right\rbrack} = {4/\left( {{SSA}\mspace{14mu} {\rho \left\lbrack {{in}\frac{g}{{cm}3}} \right\rbrack}} \right)}$

wherein SSA is the BET surface of the filtration layer in m²/g and ρ isthe density of the layer in g/cm³.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIGS. 1A-1D show cross-sections of filter media according to certainembodiments; and

FIG. 2 shows a graph of dust holding capacity versus surface averagefiber diameter for various filter media.

DETAILED DESCRIPTION

Filter media including a filtration layer (e.g., pleatable backer layer)comprising synthetic fibers and related components, systems, and methodsassociated herewith are provided. In some embodiments, the filtrationlayer may be a non-woven web (e.g., wetlaid non-woven web) comprising ablend of coarse and fine diameter synthetic fibers. The filtration layercomprising synthetic fibers may be designed to have desirableperformance properties without compromising certain mechanicalproperties, such as the pleatability of the media. For example, fibercharacteristics (e.g., diameters, composition) of the layer and relativeweight percentages in the layer may be selected to impart beneficialproperties, such as high dust holding capacity. In some embodiments, thefiltration layer may comprise a relatively high weight percentage ofsynthetic fibers and/or be substantially free of glass fibers to impartdurability and/or suitability for certain applications. In someinstances, the filtration layer comprising synthetic fibers may comprisea binder (e.g., resin, fibers) that imparts stiffness. In someembodiments, a filter media, described herein, may comprise thefiltration layer comprising synthetic fibers and an efficiency layer.Such a filter media may have a relatively high dust holding capacityand/or be pleatable. Filter media described herein may be particularlywell-suited for applications that involve filtering air, though themedia may also be used in other applications.

In some conventional filter media, desirable properties, such as highdust holding capacity and pleatability, are achieved using glass fibers.However, filter media comprising glass fibers may not be suitable forcertain applications. For instance, such filter media may not besuitable in biohazard applications that require incineration offiltration material. Moreover, in some environments, glass fibers mayleach sodium ions (e.g., Na+), which can lead to physical abrasion orsoap formation. In some instances, filter media comprising a certainamount of glass fibers may not be sufficiently durable for certain dryand humid environments.

Some existing filter media have tried to address this problem by simplyreplacing glass fibers with cellulose and/or synthetic fibers. However,in such existing filter media, a tradeoff may exist between certainperformance properties (e.g., dust holding capacity) and certainmechanical properties (e.g., durability, stiffness). Accordingly, thereis a need for filter media, especially filter media comprising arelatively low weight percentage of glass fibers or no glass fibers,that have desirable performance properties as well as mechanicalproperties.

As will be described in more detail below, a filtration layer comprisinga suitable blend of coarse and fine diameter synthetic fibers (e.g., toproduce a certain surface average fiber diameter) may have beneficialperformance properties (e.g., dust holding capacity) without comprisingcertain mechanical properties (e.g., stiffness, durability). In someembodiments, filter media comprising such a filtration layer does notsuffer from one or more limitations of existing and/or conventionalfilter media. For instance, such a filtration layer may have arelatively high dust holding capacity and have sufficient stiffness forpleatability.

In some embodiments, such a filtration layer may be a non-woven webcomprising coarse and fine diameter synthetic fibers. The fiberdiameters and relative weight percentages of the synthetic fibers may beselected such that the non-woven web has a certain surface average fiberdiameter, as described in more detail below. For instance, thefiltration layer comprising synthetic fibers may comprise greater thanor equal to about 40 wt. % of one or more coarse diameter fibers (e.g.,greater than or equal to about 15 microns) and less than or equal toabout 50 wt. % of one or more fine diameter fibers (e.g., less thanabout 15 microns) to produce a surface average fiber diameter within adesired range, e.g., greater than or equal to about 13 microns and lessthan or equal to about 17 microns. In such embodiments, the filter mediamay have a dust holding capacity of greater than or equal to about 20g/m² and/or a Gurley stiffness of, e.g., greater than or equal to about50 mg and less than or equal to about 1,500 mg in the cross direction.As described in more detail below, the filtration layer comprisingsynthetic fibers, described herein, may have a higher dust holdingcapacity and/or air permeability than a filtration layer having the samesurface average fiber diameter, but different fiber characteristics(e.g., relative weight percentage, diameter).

Non-limiting examples of filter media comprising a filtration layercomprising synthetic fibers (e.g., pleatable backer layer) are shown inFIGS. 1A-1D. In some embodiments, a filter media 10 may include afiltration layer comprising synthetic fibers 15 and a second layer 20(e.g., efficiency layer). In some embodiments, the filtration layer 15and the second layer 20 may be directly adjacent as shown in FIGS. 1Aand 1C. In other embodiments, layers 15 and 20 may be indirectlyadjacent to one another, and one or more intervening layers (e.g.,pre-filter layer) may separate the layers as illustrated in FIGS. 1B and1D. In some embodiments, filter media 10 may comprise one or moreoptional layers (e.g., pre-filter layer) positioned upstream and/ordownstream of layers 15 and 20 as illustrated in FIGS. 1B-D. Forinstance, as illustrated in FIG. 1B, in some embodiments, the filtermedia may comprise a third layer 25 downstream of the filtration layercomprising synthetic fibers (e.g., pleatable backer layer) and upstreamof the second layer. In some instances, the third layer may be directlyadjacent to the second layer (e.g., efficiency layer). In otherembodiments, layers 20 and 25 may be indirectly adjacent to one another,and one or more intervening layers may separate the layers.

Regardless of whether the filter media comprises layer 25, the filtermedia 10 may comprise a layer 30 downstream of the second layer as shownin FIG. 1D. In some instances, the layer 30 may be directly adjacent tothe second layer. In other embodiments, one or more intervening layersmay separate the layers 15 and 30. In some embodiments, filter media 10may include a filtration layer 15, a second layer 20, a third layer 25,and a fourth layer 30, as shown illustratively in FIG. 1D. In otherembodiments, filter media 10 may include a filtration layer 15, a secondlayer 20, and either a third layer 25 or a fourth layer 30.

In general, the one or more optional layers may be any suitable layer(e.g., a scrim layer, a substrate layer, an efficiency layer, a capacitylayer, a spacer layer, a support layer).

As used herein, when a layer is referred to as being “adjacent” anotherlayer, it can be directly adjacent the layer, or an intervening layeralso may be present. A layer that is “directly adjacent” another layermeans that no intervening layer is present.

In some embodiments, one or more layers in the filter media may bedesigned to be discrete from another layer. That is, the fibers from onelayer do not substantially intermingle (e.g., do not intermingle at all)with fibers from another layer. For example, with respect to FIGS.1A-1D, in one set of embodiments, fibers from the filtration layercomprising synthetic fibers do not substantially intermingle with fibersof the second layer (e.g., efficiency layer). Discrete layers may bejoined by any suitable process including, for example, lamination,thermo-dot bonding, calendering, ultrasonic processes, or by adhesives,as described in more detail below. It should be appreciated, however,that certain embodiments may include one or more layers that are notdiscrete with respect to one another.

It should be understood that the configurations of the layers shown inthe figures are by way of example only, and that in other embodiments,filter media including other configurations of layers may be possible.For example, while the first, optional second, optional third, andoptional fourth layers are shown in a specific order in FIGS. 1A-1D,other configurations are also possible. For instance, the filter mediamay comprise the filtration layer 15 and may not comprise second layer20 (e.g., efficiency layer). In some such embodiments, an article (e.g.,filter media) may consist essentially of filtration layer 15 (e.g.,pleatable backer layer). In certain embodiments, the article maycomprise filtration layer 15. It should be appreciated that the terms“second”, “third” and “fourth” layers, as used herein, refer todifferent layers within the media, and are not meant to be limiting withrespect to the location of that layer. Furthermore, in some embodiments,additional layers (e.g., “fifth”, “sixth”, or “seventh” layers) may bepresent in addition to the ones shown in the figures. It should also beappreciated that not all layers shown in the figures need be present insome embodiments.

In some embodiments, the structural features of filtration layer (e.g.,pleatable backer layer) may be selected to produce a layer that impartsbeneficial performance properties to the filter media while havingrelatively minimal or no adverse effects on another property (e.g.,stiffness) of the filter media. In certain embodiments, the filtrationlayer may have a blend of coarse and fine diameter fibers that producesa surface average fiber diameter that imparts sufficient dust holdingcapacity and/or air permeability at a relatively low basis weight. Theterm “surface average fiber diameter” is described in more detail below.In some embodiments, the filtration layer comprising synthetic fibersmay serve as a backer layer in a pleatable filter media.

For instance, in some embodiments, the filtration layer comprisingsynthetic fibers may serve as a depth filtration layer that trapparticles within the layer. In some embodiments, suitable ranges forsurface average fiber diameter, weight percentage of coarse diameterfibers, and weight percentage of fine diameter are needed to allow fordepth filtration. For example, if the surface average fiber diameter isabove the suitable range, the ability of the filtration layer comprisingsynthetic fibers to trap particles may be substantially diminished. Ifthe surface average fiber diameter is below the suitable range, thefiltration mechanism of the layer may change to surface filtration inwhich many particles are trapped on the upstream surface of the layerand, as a result, the layer may have a higher pressure drop. In someembodiments, a high pressure drop can reduce the service life of thefilter media. Without being bound by theory, it is believed that thesurface average fiber diameter may serve as a parameter that ispredictive of the efficiency and filtration mechanism of the layer (e.g.depth filtration, surface filtration).

Even if the surface average fiber diameter is within a suitable range, aweight percentage of fine diameter fibers above the suitable range mayresult in a reduction in air permeability and dust holding capacity, dueat least in part to webbing and/or bundling of the fine diameter fibersin the presence of certain binders and/or during the web manufacturingprocess. The webbing and/or bundling of the fine diameter fibers mayresult in blockage of a significant percentage of the pores in a layer.In embodiments in which the surface average fiber diameter is within asuitable range, a weight percentage of coarse diameter fibers above thesuitable range may result in a layer having a reduced capacity to trapparticles. In certain embodiments, a blend of coarse and fine diameterfibers may be needed to achieve a suitable surface average fiberdiameter.

In general, a filtration layer may comprise multiple fibers havingdifferent average fiber diameters and/or fiber diameter distributions.In such cases, the average diameter of the fibers in a layer may becharacterized using a weighted average, such as the surface averagefiber diameter. The surface average fiber diameter is defined as

d=Σ(m _(i)/ρ_(i))/Σ(m _(i) /d _(i)ρ_(i));

wherein d is the surface average fiber diameter in microns and is m_(i)the number fraction of the fibers with diameter d_(i) in microns anddensity {circumflex over (p)}_(i) in g/cm³ in the filtration layer. Theequation assumes that the fibers are cylindrical, the fibers have acircular cross-section, and that the fiber length is significantlygreater than the diameter of the fibers. It should be understood thatthe equation also provides meaningful surface average fiber diametervalues when a non-woven web includes fibers that are substantiallycylindrical and have a substantially circular cross-section.The surface average fiber diameter may be computed using the equationabove or measured, as described further below. In embodiments in whichthe diameters, densities, and mass percentages of the fibers in thefiltration layer are known, the surface average fiber diameter may becomputed.

In other embodiments, the surface average fiber diameter of thefiltration layer may be determined by measuring the BET surface averageof the filtration layer (i.e., SSA) and the density p of the layer, asdescribed in more detail below. In such cases, the surface average fiberdiameter SAFD may be determined using the modified formula below:

${{SAFD}\left\lbrack {{in}\mspace{14mu} {um}} \right\rbrack} = {4/\left( {{SSA}\mspace{14mu} {\rho \left\lbrack {{in}\frac{g}{{cm}3}} \right\rbrack}} \right)}$

wherein SSA is the BET surface of the filtration layer in m²/g and ρ isthe density of the layer in g/cm³.

As used herein, the BET surface area is measured through use of astandard BET surface area measurement technique. The BET surface area ismeasured according to section 10 of Battery Council InternationalStandard BCIS-03A, “Recommended Battery Materials Specifications ValveRegulated Recombinant Batteries”, section 10 being “Standard Test Methodfor Surface Area of Recombinant Battery Separator Mat”. Following thistechnique, the BET surface area is measured via adsorption analysisusing a BET surface analyzer (e.g., Micromeritics Gemini III 2375Surface Area Analyzer) with nitrogen gas; the sample amount is between0.5 and 0.6 grams in, e.g., a ¾″ tube; and, the sample is allowed todegas at 75 degrees C. for a minimum of 3 hours.

As used herein, the density of a layer may be determined by accuratelymeasuring the mass and volume of the layer (e.g., excluding the voidvolume) and then calculating the density of the layer. The mass of thelayer may be determined by weighing the layer. The volume of the layermay be determined using any known method of accurately measuring volume.For example, the volume may be determined using pycnometry. As anotherexample, the volume of the layer may be determined using an Archimedesmethod provided that an accurate measurement of volume is produced. Forexample, the volume may be determined by fully submerging the layer in awetting fluid and measuring the volume displacement of the wettingliquid as a result of fully submerging the layer.

In some embodiments, the filtration layer comprising synthetic fibersmay have a surface average fiber diameter of greater than or equal toabout 10 microns, greater than or equal to about 11 microns, greaterthan or equal to about 12 microns, greater than or equal to about 13microns, greater than or equal to about 14 microns, greater than orequal to about 15 microns, greater than or equal to about 16 micron,greater than or equal to about 17 microns, greater than or equal toabout 18 microns, or greater than or equal to about 19 microns. In someinstances, the surface average fiber diameter may be less than or equalto about 20 microns, less than or equal to about 19 microns, less thanor equal to about 18 microns, less than or equal to about 18 microns,less than or equal to about 17 microns, less than or equal to about 16microns, less than or equal to about 15 microns, less than or equal toabout 14 microns, less than or equal to about 13 microns, or less thanor equal to about 12 microns. All suitable combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 13 microns and less than or equal to about 17 microns, greaterthan or equal to about 14 microns and less than or equal to about 16microns). In some embodiments, a surface average fiber diameter ofgreater than or equal to about 13 microns and less than or equal toabout 17 microns may be preferred.

As noted above, the filtration layer comprising synthetic fiberscomprises a blend of coarse and fine diameter fibers that produces asuitable surface average fiber diameter. For instance, in someembodiments, the filtration layer comprising synthetic fibers maycomprise a relatively high weight percentage of coarse diameter fibers(e.g., greater than or equal to about 40 wt. %). In certain embodiments,the total weight percentage of coarse diameter fibers in the filtrationlayer comprising synthetic fibers and/or in the total weight percentageof coarse diameter fibers of all fibers in the filtration layer may begreater than or equal to about 10 wt. %, greater than or equal to about20 wt. %, greater than or equal to about 30 wt. %, greater than or equalto about 40 wt. %, greater than or equal to about 50 wt. %, greater thanor equal to about 60 wt. %, greater than or equal to about 70 wt. %,greater than or equal to about 80 wt. %, or greater than or equal toabout 85 wt. %. In some instances, the total weight percentage of coarsediameter fibers in the filtration layer comprising synthetic fibersand/or in the total weight percentage of coarse diameter fibers of allfibers in the filtration layer may be less than or equal to about 90 wt.%, less than or equal to about 80 wt. %, less than or equal to about 70wt. %, less than or equal to about 60 wt. %, less than or equal to about50 wt. %, less than or equal to about 40 wt. %, less than or equal toabout 30 wt. %, less than or equal to about 20 wt. %, or less than orequal to about 15 wt. %. All suitable combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 10 wt. % and less than or equal to about 90 wt. %, greater thanor equal to about 40 wt. % and less than or equal to about 80 wt. %). Insome embodiments, a total weight percentage of coarse diameter fibers ofgreater than or equal to about 40 wt. % may be preferred.

In some embodiments, the total weight percentage of coarse diameterfibers in the filtration layer comprising synthetic fibers and/or in thetotal weight percentage of coarse diameter fibers of all fibers in thefiltration layer may include two or more populations of coarse diameterfibers having a different average fiber diameter. For instance, afiltration layer comprising synthetic fibers having a total weightpercentage of coarse diameter fibers of greater than or equal to about40 wt. % and less than or equal to about 80 wt. % may comprise a firstpopulation of coarse diameter fibers having an average fiber diameter ofgreater than or equal to about 15 microns and less than or equal toabout 25 microns at a weight percentage of greater than or equal toabout 5 wt. % and less than or equal to about 95 wt. % (e.g., greaterthan or equal to about 10 wt. % and less than or equal to about 60 wt.%) and a second population of coarse diameter fibers having an averagefiber diameter of greater than or equal to about 25 microns and lessthan or equal to about 50 microns at a weight percentage of greater thanor equal to about 5 wt. % and less than or equal to about 95 wt. %(e.g., greater than or equal to about 10 wt. % and less than or equal toabout 60 wt. %). In certain embodiments, a blend of coarse diameterfibers may be used to help achieve the desired surface average fiberdiameter. In general, any suitable number of coarse diameter fiberpopulations having different average fiber diameters may be used. Inother embodiments, the total weight percentage of coarse diameter fibersis composed of one population of coarse diameter fibers. That is, thelayer does not comprise two or more populations of coarse diameterfibers having a different average fiber diameter.

In some embodiments, coarse diameter fibers used in the filtration layercomprising synthetic fibers may have an average fiber of diametergreater than or equal to about 15 microns, greater than or equal toabout 17 microns, greater than or equal to about 20 microns, greaterthan or equal to about 25 microns, greater than or equal to about 30microns, greater than or equal to about 35 microns, greater than orequal to about 40 micron, greater than or equal to about 45 microns,greater than or equal to about 50 microns, or greater than or equal toabout 55 microns. In some instances, the average fiber diameter may beless than or equal to about 60 microns, less than or equal to about 55microns, less than or equal to about 50 microns, less than or equal toabout 45 microns, less than or equal to about 40 microns, less than orequal to about 35 microns, less than or equal to about 30 microns, lessthan or equal to about 25 microns, less than or equal to about 20microns, or less than or equal to about 17 microns. All suitablecombinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 10 microns and less than or equal toabout 60 microns, greater than or equal to about 17 microns and lessthan or equal to about 35 microns).

In some embodiments, the coarse diameter fibers in the filtration layercomprising synthetic fibers may have an average length of greater thanor equal to about 3 mm, greater than or equal about 6 mm, greater thanor equal about 9 mm, greater than or equal about 12 mm, greater than orequal about 15 mm, greater than or equal about 18 mm, greater than orequal about 20 mm, greater than or equal about 22 mm, or greater than orequal about 25 mm. In some instances, the average length of the coarsediameter fibers may be less than or equal to about 30 mm, less than orequal to about 27 mm, less than or equal to about 25 mm, less than orequal to about 22 mm, less than or equal to about 20 mm, less than orequal to about 18 mm, less than or equal to about 15 mm, less than orequal to about 12 mm, less than or equal to about 9 mm, or less than orequal to about 6 mm. All suitable combinations of the above-referencedranges are also possible (e.g., greater than or equal about 3 mm andless than or equal to about 30 mm, greater than or equal about 6 mm andless than or equal to about 12 mm).

As noted above, the filtration layer comprising synthetic fibers maycomprise a blend of coarse diameter fibers and fine diameter fibers toproduce a suitable surface average fiber diameter. In certainembodiments, the total weight percentage of fine diameter fibers in thefiltration layer comprising synthetic fibers and/or in the total weightpercentage of fine diameter fibers of all fibers in the filtration layermay be less than or equal to about 50 wt. %, less than or equal to about45 wt. %, less than or equal to about 40 wt. %, less than or equal toabout 35 wt. %, less than or equal to about 30 wt. %, less than or equalto about 25 wt. %, less than or equal to about 20 wt. %, or less than orequal to about 15 wt. %. In some instances, the total weight percentageof fine diameter fibers in the filtration layer comprising syntheticfibers and/or in the total weight percentage of fine diameter fibers ofall fibers in the filtration layer may be greater than or equal to about0.5 wt. %, greater than or equal to about 5 wt. %, greater than or equalto about 10 wt. %, greater than or equal to about 15 wt. %, greater thanor equal to about 20 wt. %, greater than or equal to about 25 wt. %,greater than or equal to about 30 wt. %, greater than or equal to about35 wt. %, greater than or equal to about 40 wt. %, or greater than orequal to about 45 wt. %. All suitable combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 0.5 wt. % and less than or equal to about 50 wt. %, greaterthan or equal to about 10 wt. % and less than or equal to about 30 wt.%).

In some embodiments, the total weight percentage of fine diameter fibersin the filtration layer comprising synthetic fibers and/or in the totalweight percentage of fine diameter fibers of all fibers in thefiltration layer may include two or more populations of fine diameterfibers having a different average fiber diameter. For instance, afiltration layer comprising synthetic fibers having a total weightpercentage of fine diameter fibers of greater than or equal to about 10wt. % and less than or equal to about 30 wt. % may comprise a firstpopulation of fine diameter fibers having an average fiber diameter ofgreater than or equal to about 0.1 microns and less than or equal toabout 10 microns at a weight percentage of greater than or equal toabout 5 wt. % and less than or equal to about 95 wt. % (e.g., greaterthan or equal to about 10 wt. % and less than or equal to about 60 wt.%) and a second population of fine diameter fibers having an averagefiber diameter of greater than or equal to about 10 microns and lessthan about 15 microns at a weight percentage of greater than or equal toabout 5 wt. % and less than or equal to about 95 wt. % (e.g., greaterthan or equal to about 10 wt. % and less than or equal to about 60 wt.%). In certain embodiments, the blend of fine diameter fibers may beused to help achieve the desired surface average fiber diameter. Ingeneral, any suitable number of fine fiber populations having differentaverage fiber diameters may be used. In other embodiments, the totalweight percentage of fine diameter fibers is composed of one populationof fine diameter fibers. That is, the layer does not comprise two ormore populations of fine diameter fibers having a different averagefiber diameter.

In some embodiments, fine diameter fibers used in the filtration layercomprising synthetic fibers may have an average fiber diameter of lessthan about 15 microns, less than or equal to about 12 microns, less thanor equal to about 10 microns, less than or equal to about 8 microns,less than or equal to about 6 microns, less than or equal to about 5microns, less than or equal to about 4 microns, less than or equal toabout 3 microns, less than or equal to about 2 microns, or less than orequal to about 1 micron. In some instances, the average fiber diametermay be greater than or equal to about 0.5 microns, greater than or equalto about 1 micron, greater than or equal to about 2 microns, greaterthan or equal to about 3 microns, greater than or equal to about 4microns, greater than or equal to about 5 microns, greater than or equalto about 6 microns, greater than or equal to about 8 microns, greaterthan or equal to about 10 microns, or greater than or equal to about 12microns. All suitable combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to about 0.5 microns and lessthan about 15 microns, greater than or equal to about 2 microns and lessthan or equal to about 10 microns).

In some embodiments, the fine diameter fibers in the filtration layercomprising synthetic fibers may have an average length of greater thanor equal to about 0.1 mm, greater than or equal to about 0.3 mm, greaterthan or equal to about 0.5 mm, greater than or equal to about 0.8 mm,greater than or equal to about 1 mm, greater than or equal to about 3mm, greater than or equal about 6 mm, greater than or equal about 9 mm,greater than or equal about 12 mm, greater than or equal about 15 mm,greater than or equal about 18 mm, greater than or equal about 20 mm,greater than or equal about 22 mm, or greater than or equal about 25 mm.In some instances, the average length of the fine diameter fibers may beless than or equal to about 30 mm, less than or equal to about 27 mm,less than or equal to about 25 mm, less than or equal to about 22 mm,less than or equal to about 20 mm, less than or equal to about 18 mm,less than or equal to about 15 mm, less than or equal to about 12 mm,less than or equal to about 9 mm, less than or equal to about 6 mm, lessthan or equal to about 3 mm, or less than or equal to about 1 mm. Allsuitable combinations of the above-referenced ranges are also possible(e.g., greater than or equal about 0.1 mm and less than or equal toabout 30 mm, greater than or equal about 0.3 mm and less than or equalto about 12 mm).

In some embodiments, the coarse and/or fine diameter fibers are notglass fibers. In certain embodiments, a relatively high weightpercentage of the total coarse and/or fine diameter fibers thefiltration layer comprising synthetic fibers may be synthetic fibers.For instance, in some embodiments, the weight percentage of syntheticfibers of all fibers in the filtration layer may be greater than orequal to about 80 wt. %, greater than or equal to about 85 wt. %,greater than or equal to about 88 wt. %, greater than or equal to about90 wt. %, greater than or equal to about 92 wt. %, greater than or equalto about 95 wt. %, greater than or equal to about 97 wt. %, or greaterthan or equal to about 99 wt. %. In some embodiments, the filtrationlayer comprising synthetic fibers may include 100 wt. % syntheticfibers. In some embodiments, the filtration layer comprising syntheticfibers may be substantially free of glass fibers.

In certain embodiments, the weight percentage of coarse synthetic fibersof all coarse diameter fibers in the filtration layer comprisingsynthetic fibers may be greater than or equal to about 80 wt. %, greaterthan or equal to about 85 wt. %, greater than or equal to about 88 wt.%, greater than or equal to about 90 wt. %, greater than or equal toabout 92 wt. %, greater than or equal to about 95 wt. %, greater than orequal to about 97 wt. %, or greater than or equal to about 99 wt. %. Incertain embodiments, the weight percentage of coarse synthetic fibers ofall coarse diameter fibers in the filtration layer comprising syntheticfibers may be 100 wt. %. In some embodiments, the weight percentage ofsynthetic fibers of all fine diameter fibers in the filtration layercomprising synthetic fibers may be greater than or equal to about 80 wt.%, greater than or equal to about 85 wt. %, greater than or equal toabout 88%, greater than or equal to about 90 wt. %, greater than orequal to about 92 wt. %, greater than or equal to about 95 wt. %,greater than or equal to about 97 wt. %, or greater than or equal toabout 99 wt. %. In some embodiments, the weight percentage of syntheticfibers of all fine diameter fibers in the filtration layer comprisingsynthetic fibers may be 100 wt. %.

In general, synthetic fibers may include any suitable type of syntheticpolymer. Examples of suitable synthetic fibers include polyesters (e.g.,polyethylene terephthalate, polybutylene terephthalate), polycarbonate,polyamides (e.g., various nylon polymers), polyaramid, polyimide,polyethylene, polypropylene, polyether ether ketone, polyolefin,acrylics, polyvinyl alcohol, regenerated cellulose (e.g., syntheticcellulose such lyocell, rayon), polyacrylonitriles, polyvinylidenefluoride (PVDF), copolymers of polyethylene and PVDF, polyethersulfones, and combinations thereof. In some embodiments, the syntheticfibers are organic polymer fibers. Synthetic fibers may also includemulticomponent fibers (i.e., fibers having multiple compositions such asbicomponent fibers). In some cases, synthetic fibers may includemeltblown, meltspun, electrospun (e.g., melt, solvent), or centrifugalspun fibers, which may be formed of polymers described herein (e.g.,polyester, polypropylene). In some embodiments, synthetic fibers may bestaple fibers. In some embodiments, the synthetic fibers may be flameretardant fibers. The filter media, as well as each of the layers withinthe filter media, may also include combinations of more than one type ofsynthetic fiber. It should be understood that other types of syntheticfibers may also be used.

In some embodiments, the filtration layer comprising synthetic fibersmay include flame retardant fibers, such as phosphoric-containingfibers, nitrogen-containing fibers, and/or halogen-containing fibers. Insome embodiments, the flame retardant fibers may be synthetic fibers. Ingeneral, the total weight percentage of coarse and/or fine diameterfibers may include flame retardant fibers. In some embodiments, thetotal weight percentage of flame retardant fibers in the filtrationlayer comprising synthetic fibers and/or in the total weight percentageof flame retardant fibers of all fibers in the filtration layer may begreater than or equal to about 0.5 wt. %, greater than or equal to about1 wt. %, greater than or equal to about 5 wt. %, greater than or equalto about 10 wt. %, greater than or equal to about 20 wt. %, greater thanor equal to about 30 wt. %, greater than or equal to about 40 wt. %,greater than or equal to about 50 wt. %, greater than or equal to about60 wt. %, greater than or equal to about 70 wt. %, greater than or equalto about 80 wt. %, or greater than or equal to about 90 wt. %. In someinstances, total weight percentage may be less than or equal to about100 wt. %, less than or equal to about 90 wt. %, less than or equal toabout 80 wt. %, less than or equal to about 70 wt. %, less than or equalto about 60 wt. %, less than or equal to about 50 wt. %, less than orequal to about 40 wt. %, less than or equal to about 30 wt. %, less thanor equal to about 20 wt. %, less than or equal to about 15 wt. %, lessthan or equal to about 10 wt. %, or less than or equal to about 5 wt. %.All suitable combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to about 0.5 wt. % and less thanor equal to about 100 wt. %). In other embodiments, the filtration layercomprising synthetic fibers may comprise 0 wt. % of flame retardantfibers.

In some embodiments, the filtration layer comprising synthetic fibersmay comprise one or more binders (e.g., binder resin, binder fiber) thatserves to impart structural integrity to the filtration layer, as wellas provide important mechanical properties, such as Gurley stiffness,Mullen burst, and/or tensile strength, to the media.

In some embodiments, the binder may be one or more binder fibers. Ingeneral, binder fibers may be used to join fibers within the layer. Insome embodiments, binder fibers comprise polymers with a lower meltingpoint than one or more major component in the layer, such as certainfibers. Binder fibers may be monocomponent (e.g., polyethylene fibers,copolyester fibers) or multicomponent (e.g., bicomponent fibers). Forexample, a binder fiber may be a bicomponent fiber. The bicomponentfibers may comprise a thermoplastic polymer. Each component of thebicomponent fiber can have a different melting temperature. For example,the fibers can include a core and a sheath where the activationtemperature of the sheath is lower than the melting temperature of thecore. This allows the sheath to melt prior to the core, such that thesheath binds to other fibers in the layer, while the core maintains itsstructural integrity. The core/sheath binder fibers can be concentric ornon-concentric. Other exemplary bicomponent fibers can include splitfiber fibers, side-by-side fibers, and/or “island in the sea” fibers. Ingeneral, the total weight percentage of coarse and/or fine diameterfibers may include binder fibers.

In some embodiments, the binder may be one or more binder resins. Ingeneral, binder resin may be used to join fibers within the layer. Ingeneral, the binder resin may have any suitable composition. Forexample, the binder resin may comprise a thermoplastic (e.g., acrylic,polyvinylacetate, polyester, polyamide), a thermoset (e.g., epoxy,phenolic resin), or a combination thereof. In some cases, a binder resinincludes one or more of a vinyl acetate resin, an epoxy resin, apolyester resin, a copolyester resin, a polyvinyl alcohol resin, anacrylic resin such as a styrene acrylic resin, and a phenolic resin.Other resins are also possible.

As described further below, the resin may be added to the fibers in anysuitable manner including, for example, in the wet state. In someembodiments, the resin coats the fibers and is used to adhere fibers toeach other to facilitate adhesion between the fibers. Any suitablemethod and equipment may be used to coat the fibers, for example, usingcurtain coating, gravure coating, melt coating, dip coating, knife rollcoating, or spin coating, amongst others. In some embodiments, thebinder is precipitated when added to the fiber blend. When appropriate,any suitable precipitating agent (e.g., Epichlorohydrin, fluorocarbon)may be provided to the fibers, for example, by injection into the blend.In some embodiments, upon addition to the fibers, the resin is added ina manner such that one or more layer or the entire filter media isimpregnated with the resin (e.g., the resin permeates throughout). In amulti-layered web, a resin may be added to each of the layers separatelyprior to combining the layers, or the resin may be added to the layerafter combining the layers. In some embodiments, resin is added to thefibers while in a dry state, for example, by spraying or saturationimpregnation, or any of the above methods. In other embodiments, a resinis added to a wet layer.

In certain embodiments, the binder may comprise both binder fibers andbinder resin.

Regardless of whether the binder is a binder fiber, binder resin, orboth, the total weight percentage of binder in the filtration layercomprising synthetic fibers may be greater than or equal to about 0.5wt. %, greater than or equal to about 1 wt. %, greater than or equal toabout 5 wt. %, greater than or equal to about 10 wt. %, greater than orequal to about 20 wt. %, greater than or equal to about 30 wt. %,greater than or equal to about 40 wt. %, greater than or equal to about50 wt. %, greater than or equal to about 60 wt. %, greater than or equalto about 70 wt. %, or greater than or equal to about 80 wt. %. In someinstances, total weight percentage may be less than or equal to about 90wt. %, less than or equal to about 80 wt. %, less than or equal to about70 wt. %, less than or equal to about 60 wt. %, less than or equal toabout 50 wt. %, less than or equal to about 40 wt. %, less than or equalto about 30 wt. %, less than or equal to about 20 wt. %, less than orequal to about 15 wt. %, less than or equal to about 10 wt. %, or lessthan or equal to about 5 wt. %. All suitable combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 0.5 wt. % and less than or equal to about 90 wt. %, greaterthan or equal to about 5 wt. % and less than or equal to about 15 wt.%).

In embodiments in which the binder comprises binder fiber and optionallybinder resin, the total weight percentage of binder fiber (e.g.,bicomponent fiber) in the filtration layer comprising synthetic fibersmay be greater than or equal to about 0.5 wt. %, greater than or equalto about 1 wt. %, greater than or equal to about 3 wt. %, greater thanor equal to about 5 wt. %, greater than or equal to about 8 wt. %,greater than or equal to about 10 wt. %, greater than or equal to about20 wt. %, greater than or equal to about 25 wt. %, greater than or equalto about 30 wt. %, greater than or equal to about 40 wt. %, greater thanor equal to about 50 wt. %, greater than or equal to about 60 wt. %,greater than or equal to about 70 wt. %, or greater than or equal toabout 80 wt. %. In some instances, total weight percentage of binderfiber (e.g., bicomponent fiber) may be less than or equal to about 90wt. %, less than or equal to about 80 wt. %, less than or equal to about70 wt. %, less than or equal to about 60 wt. %, less than or equal toabout 50 wt. %, less than or equal to about 40 wt. %, less than or equalto about 30 wt. %, less than or equal to about 25 wt. %, less than orequal to about 20 wt. %, less than or equal to about 18 wt. %, less thanor equal to about 15 wt. %, less than or equal to about 12 wt. %, lessthan or equal to about 10 wt. %, less than or equal to about 8 wt. %,less than or equal to about 5 wt. %, less than or equal to about 3 wt.%, or less than or equal to about 1 wt. %. All suitable combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to about 0.5 wt. % and less than or equal to about 90 wt. %,greater than or equal to about 5 wt. % and less than or equal to about15 wt. %, greater than or equal to about 0.5 wt. % and less than orequal to about 10 wt. %). In some embodiments, one or more layers (e.g.,filtration layer comprising synthetic fibers, second layer) and/or theentire filter media may include a relatively low percentage (e.g., lessthan or equal to about 10 wt. %, less than or equal to about 5 wt. %,less than or equal to about 1 wt. %, 0 wt. %) of binder fibers (e.g.,bicomponent fibers).

In embodiments in which the binder comprises binder resin and optionallybinder fiber, the total weight percentage of binder resin in thefiltration layer comprising synthetic fibers may be greater than orequal to about 0.5 wt. %, greater than or equal to about 1 wt. %,greater than or equal to about 3 wt. %, greater than or equal to about 5wt. %, greater than or equal to about 8 wt. %, greater than or equal toabout 10 wt. %, greater than or equal to about 20 wt. %, greater than orequal to about 25 wt. %, greater than or equal to about 30 wt. %,greater than or equal to about 40 wt. %, greater than or equal to about50 wt. %, greater than or equal to about 60 wt. %, greater than or equalto about 70 wt. %, or greater than or equal to about 80 wt. %. In someinstances, total weight percentage of binder resin may be less than orequal to about 90 wt. %, less than or equal to about 80 wt. %, less thanor equal to about 70 wt. %, less than or equal to about 60 wt. %, lessthan or equal to about 50 wt. %, less than or equal to about 40 wt. %,less than or equal to about 30 wt. %, less than or equal to about 25 wt.%, less than or equal to about 20 wt. %, less than or equal to about 18wt. %, less than or equal to about 15 wt. %, less than or equal to about12 wt. %, less than or equal to about 10 wt. %, less than or equal toabout 8 wt. %, less than or equal to about 5 wt. %, less than or equalto about 3 wt. %, or less than or equal to about 1 wt. %. All suitablecombinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 0.5 wt. % and less than or equal to about90 wt. %, greater than or equal to about 5 wt. % and less than or equalto about 15 wt. %).

In some embodiments, binder fibers used in the filtration layercomprising synthetic fibers may have a fiber diameter greater than orequal to about 1 micron, greater than or equal to about 2 microns,greater than or equal to about 5 microns, greater than or equal to about8 microns, greater than or equal to about 10 microns, greater than orequal to about 12 microns, greater than or equal to about 15 micron,greater than or equal to about 18 microns, greater than or equal toabout 20 microns, greater than or equal to about 22 microns, or greaterthan or equal to about 25 microns. In some instances, the fiber diametermay be less than or equal to about 30 microns, less than or equal toabout 28 microns, less than or equal to about 25 microns, less than orequal to about 22 microns, less than or equal to about 20 microns, lessthan or equal to about 18 microns, less than or equal to about 15microns, less than or equal to about 12 microns, less than or equal toabout 10 microns, less than or equal to about 5 microns, or less than orequal to about 2 microns. All suitable combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 1 micron and less than or equal to about 30 microns, greaterthan or equal to about 2 microns and less than or equal to about 20microns).

In some embodiments, the binder fibers in the filtration layercomprising synthetic fibers may have an average length of greater thanor equal to about 3 mm, greater than or equal about 6 mm, greater thanor equal about 9 mm, greater than or equal about 12 mm, greater than orequal about 15 mm, greater than or equal about 18 mm, greater than orequal about 20 mm, greater than or equal about 22 mm, or greater than orequal about 25 mm. In some instances, the average length of the binderfibers may be less than or equal to about 30 mm, less than or equal toabout 27 mm, less than or equal to about 25 mm, less than or equal toabout 22 mm, less than or equal to about 20 mm, less than or equal toabout 18 mm, less than or equal to about 15 mm, less than or equal toabout 12 mm, less than or equal to about 9 mm, or less than or equal toabout 6 mm. All suitable combinations of the above-referenced ranges arealso possible (e.g., greater than or equal about 3 mm and less than orequal to about 30 mm, greater than or equal about 6 mm and less than orequal to about 12 mm).

As described herein, filter media 10 may include a filtration layercomprising synthetic fibers. In some embodiments, the filtration layercomprising synthetic fibers may have certain enhanced mechanicalproperties, such as Gurley stiffness, tensile strength, and/or MullenBurst strength. In general, the filtration layer comprising syntheticfibers may provide sufficient Gurley stiffness such that the filtermedia can be pleated to include sharp, well-defined peaks which can bemaintained in a stable configuration during use.

The filtration layer comprising synthetic fibers may have a relativelyhigh Gurley stiffness. For instance, in some embodiments, the filtrationlayer comprising synthetic fibers may have a Gurley stiffness in thecross direction of greater than or equal to about 50 mg, greater than orequal to about 100 mg, greater than or equal to about 200 mg, greaterthan or equal to about 300 mg, greater than or equal to about 500 mg,greater than or equal to about 800 mg, greater than or equal to about1,000 mg, greater than or equal to about 1,200 mg, or greater than orequal to about 1,400 mg. In some embodiments, the filtration layercomprising synthetic fibers may have a Gurley stiffness in the crossdirection of less than or equal to about 1,500 mg, less than or equal toabout 1,400 mg, less than or equal to about 1,200 mg, less than or equalto about 1,000 mg, less than or equal to about 800 mg, less than orequal to about 500 mg, less than or equal to about 300 mg, less than orequal to about 200 mg, or less than or equal to about 100 mg. Allsuitable combinations of the above-referenced ranges are also possible(e.g., greater than or equal to about 50 mg and less than or equal toabout 1,500 mg, greater than or equal to about 200 mg and less than orequal to about 1,000 mg). The stiffness may be determined using theGurley stiffness (bending resistance) recorded in units of mm(equivalent to gu) in accordance with TAPPI T543 om-94.

In some embodiments, the filtration layer comprising synthetic fibersmay have a Gurley stiffness in the machine direction of greater than orequal to about 200 mg, greater than or equal to about 350 mg, greaterthan or equal to about 500 mg, greater than or equal to about 750 mg,greater than or equal to about 1,000 mg, greater than or equal to about1,500 mg, greater than or equal to about 2,000 mg, greater than or equalto about 2,500 mg, or greater than or equal to about 3,000 mg. In someembodiments, the filtration layer comprising synthetic fibers may have aGurley stiffness in the machine direction of less than or equal to about3,500 mg, less than or equal to about 3,000 mg, less than or equal toabout 2,500 mg, less than or equal to about 2,000 mg, less than or equalto about 1,500 mg, less than or equal to about 1,000 mg, less than orequal to about 750 mg, or less than or equal to about 500 mg. Allsuitable combinations of the above-referenced ranges are also possible(e.g., greater than or equal to about 200 mg and less than or equal toabout 3,500 mg, greater than or equal to about 350 mg and less than orequal to about 2,000 mg).

In some embodiments, the filtration layer comprising synthetic fibersmay have a dry tensile strength in the machine direction (MD) of greaterthan or equal to about 2 lb/in, greater than or equal to about 4 lb/in,greater than or equal to about 5 lb/in, greater than or equal to about10 lb/in, greater than or equal to about 15 lb/in, greater than or equalto about 20 lb/in, greater than or equal to about 30 lb/in, greater thanor equal to about 40 lb/in, greater than or equal to about 50 lb/in, orgreater than or equal to about 55 lb/in. In some instances, the drytensile strength in the machine direction may be less than or equal toabout 60 lb/in, less than or equal to about 50 lb/in, less than or equalto about 40 lb/in, less than or equal to about 30 lb/in, less than orequal to about 20 lb/in, less than or equal to about 10 lb/in, or lessthan or equal to about 5 lb/in. All suitable combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 2 lb/in and less than or equal to about 60 lb/in, greater thanor equal to about 10 lb/in and less than or equal to about 40 lb/in).Other values of dry tensile strength in the machine direction are alsopossible. The dry tensile strength in the machine direction may bedetermined according to the standard T494 om-96 using a test span of 4in and a jaw separation speed of 1 in/min.

In some embodiments, the filtration layer comprising synthetic fibersmay have a dry tensile strength in the cross direction (CD) of greaterthan or equal to about 1 lb/in, greater than or equal to about 2 lb/in,greater than or equal to about 5 lb/in, greater than or equal to about 6lb/in, greater than or equal to about 8 lb/in, greater than or equal toabout 10 lb/in, greater than or equal to about 12 lb/in, greater than orequal to about 15 lb/in, or greater than or equal to about 18 lb/in. Insome instances, the dry tensile strength in the cross direction may beless than or equal to about 20 lb/in, less than or equal to about 18lb/in, less than or equal to about 15 lb/in, less than or equal to about12 lb/in, less than or equal to about 10 lb/in, less than or equal toabout 8 lb/in, less than or equal to about 6 lb/in, or less than orequal to about 5 lb/in. All suitable combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 1 lb/in and less than or equal to about 20 lb/in, greater thanor equal to about 6 lb/in and less than or equal to about 15 lb/in).Other values of dry tensile strength in the cross direction are alsopossible. The dry tensile strength in the cross direction may bedetermined according to the standard T494 om-96 using a test span of 4in and a jaw separation speed of 1 in/min.

In some embodiments, the filtration layer comprising synthetic fibersmay have a dry Mullen Burst strength of greater than or equal to about 5psi, greater than or equal to about 20 psi, greater than or equal toabout 25 psi, greater than or equal to about 30 psi, greater than orequal to about 50 psi, greater than or equal to about 75 psi, greaterthan or equal to about 100 psi, greater than or equal to about 125 psi,greater than or equal to about 150 psi, greater than or equal to about175 psi, greater than or equal to about 200 psi, greater than or equalto about 225 psi, or greater than or equal to about 240 psi. In someinstances, the dry Mullen Burst strength may be less than or equal toabout 250 psi, less than or equal to about 240 psi, less than or equalto about 225 psi, less than or equal to about 200 psi, less than orequal to about 175 psi, less than or equal to about 150 psi, less thanor equal to about 125 psi, less than or equal to about 100 psi, lessthan or equal to about 75 psi, less than or equal to about 50 psi, orless than or equal to about 25 psi. All suitable combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 20 psi and less than or equal to about 250 psi, greater than orequal to about 30 psi and less than or equal to about 150 psi). Othervalues of dry Mullen Burst strength are also possible. The dry MullenBurst strength may be determined according to the standard T403 om-91.

In some embodiments, filtration layer 15 may have a relatively high airpermeability. For instance, in some embodiments, the air permeability ofthe filtration layer comprising synthetic fibers may be greater than orequal to about 50 ft³/min/ft² (CFM), greater than or equal to about 75CFM, greater than or equal to about 100 CFM, greater than or equal toabout 150 CFM, greater than or equal to about 200 CFM, greater than orequal to about 250 CFM, greater than or equal to about 300 CFM, greaterthan or equal to 350 CFM, greater than or equal to about 400 CFM,greater than or equal to about 450 CFM, greater than or equal to about500 CFM, greater than or equal to 550 CFM, greater than or equal toabout 600 CFM, greater than or equal to about 650 CFM, greater than orequal to about 700 CFM, or greater than or equal to about 750 CFM. Insome instances, the air permeability of the filtration layer comprisingsynthetic fibers may be less than or equal to about 800 CFM, less thanor equal to about 750 CFM, less than or equal to about 700 CFM, lessthan or equal to about 650 CFM, less than or equal to about 600 CFM,less than or equal to about 550 CFM, less than or equal to about 500CFM, less than or equal to about 450 CFM, less than or equal to about400 CFM, less than or equal to about 350 CFM, less than or equal toabout 300 CFM, less than or equal to about 250 CFM, less than or equalto about 200 CFM, less than or equal to about 150 CFM, or less than orequal to about 100 CFM. It should be understood that all suitablecombinations of the above-referenced ranges are possible (e.g., greaterthan or equal to about 50 CFM and less than or equal to about 800 CFM,greater than or equal to about 200 CFM and less than or equal to about500 CFM).

As used herein, air permeability is measured according to the standardASTM D737-75. In the air permeability testing apparatus, the sample isclamped on to a test head which provides a circular test area of 38.3cm² referred to as nozzle, at a force of at least 50+/−5 N withoutdistorting the sample and with minimum edge leakage. A steady flow ofair perpendicular to the sample test area is then supplied providing apressure differential of 12.5 mm H₂O across the material being tested.This pressure differential is recorded from the pressure gauge ormanometer connected to the test head. The air permeability through thetest area is measured in ft³/min/ft² using a flow meter or volumetriccounter. A Frazier air permeability tester is an example apparatus forsuch a measurement.

In some embodiments, the filtration layer comprising synthetic fibersmay have a relatively small basis weight. For instance, in someembodiments, the filtration layer may have a basis weight of less thanor equal to about 110 g/m², less than or equal to about 100 g/m², lessthan or equal to about 97 g/m², less than or equal to about 95 g/m²,less than or equal to about 92 g/m², less than or equal to about 90g/m², less than or equal to about 87 g/m², less than or equal to about85 g/m², less than or equal to about 82 g/m², less than or equal toabout 80 g/m², less than or equal to about 70 g/m², less than or equalto about 60 g/m², less than or equal to about 50 g/m², less than orequal to about 40 g/m², or less than or equal to about 30 g/m². In someinstances, the filtration layer comprising synthetic fibers may have abasis weight of greater than or equal to about 20 g/m², greater than orequal to about 30 g/m², greater than or equal to about 40 g/m², greaterthan or equal to about 50 g/m², greater than or equal to about 60 g/m²,greater than or equal to about 70 g/m², greater than or equal to about80 g/m², greater than or equal to about 90 g/m², or greater than orequal to about 100 g/m². All suitable combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 20 g/m² and less than or equal to about 110 g/m², greater thanor equal to about 20 g/m² and less than or equal to about 90 g/m²).Other values of basis weight are also possible. The basis weight may bedetermined according to the standard ASTM D-13776.

In some embodiments, the filtration layer comprising synthetic fibersmay be relatively thin. For instance, in some embodiments, thefiltration layer comprising synthetic fibers may have a thickness ofless than or equal to about 2.0 mm, less than or equal to about 1.8 mm,less than or equal to about 1.5 mm, less than or equal to about 1.2 mm,less than or equal to about 1.0 mm, less than or equal to about 0.8 mm,less than or equal to about 0.7 mm, less than or equal to about 0.6 mm,or less than or equal to about 0.5 mm, or less than or equal to about0.4 mm. In some instances, the filtration layer comprising syntheticfibers may have a thickness of greater than or equal to about 0.25 mm,greater than or equal to about 0.3 mm, greater than or equal to about0.4 mm, greater than or equal to about 0.5 mm, greater than or equal toabout 0.6 mm, greater than or equal to about 0.8 mm, greater than orequal to about 1.0 mm, greater than or equal to about 1.2 mm, greaterthan or equal to about 1.5 mm, or greater than or equal to about 1.8 mm.All suitable combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to about 0.25 mm and less than orequal to about 2.0 mm, greater than or equal to about 0.4 mm and lessthan or equal to about 1.0 mm, greater than or equal to about 0.25 mmand less than or equal to about 0.7 mm, greater than or equal to about0.4 mm and less than or equal to about 0.8 mm). The thickness isdetermined according to the standard ASTM D1777 at 0.3 psi.

As noted above, the filter media may include a second layer. In someembodiments, the second layer functions to enhance particle captureefficiency of the filter media, and may be referred to as an efficiencylayer. Typically, the efficiency layer does not include a spacer layer(e.g., spun-bond layer) when referring to the structural and performancecharacteristics of the efficiency layer, and/or the number of layerswithin the efficiency layer.

In general, the average efficiency of the second layer and/or the entirefilter media may vary based on the application. In some embodiments, thesecond layer and/or the entire filter media may have DEHS averageefficiency at 0.4 microns of greater than or equal to about 10%, greaterthan or equal to about 20%, greater than or equal to about 35%, greaterthan or equal to about 50%, greater than or equal to about 60%, greaterthan or equal to about 70%, greater than or equal to about 80%, greaterthan or equal to about 90%, greater than or equal to about 95%, greaterthan or equal to about 97%, greater than or equal to about 99%, greaterthan or equal to about 99.5%, greater than or equal to about 99.9%,greater than or equal to about 99.95%, greater than or equal to about99.99%, greater than or equal to about 99.995%, greater than or equal to99.999%, greater than or equal to 99.9999%, or greater than or equal to99.99999%. In some instances, the second layer and/or the entire filtermedia may have DEHS average efficiency at 0.4 microns of less than orequal to 99.99999%, less than or equal to 99.9999%, less than or equalto about 99.999%, less than or equal to about 99.99%, less than or equalto about 99.997%, less than or equal to about 99.995%, less than orequal to about 99.9%, less than or equal to about 99.5%, less than orequal to about 99%, less than or equal to about 98%, less than or equalto about 97%, less than or equal to about 95%, less than or equal toabout 90%, less than or equal to about 85%, less than or equal to about75%, less than or equal to about 60%, less than or equal to about 50%,less than or equal to about 40%, less than or equal to about 30%, lessthan or equal to about 20%, or less than or equal to about 10%. Itshould be understood that all suitable combinations of theabove-referenced ranges are possible (e.g., greater than or equal toabout 20% and less than or equal to about 99.99999%). The DEHS averageefficiency may be measured according to EN1822, and for efficiencies<90%, may be measured according to EN779:2012. In some embodiments, theaverage efficiency of a layer (e.g., second layer) and/or a filter mediamay be tested following the EN779-2012 standard. The testing uses an airflow of 0.944 m³/s (3400 m³/h) and a maximum final test pressure drop of250 Pa (e.g., for Coarse or G filter media) or a maximum final testpressure drop of 450 Pa (e.g., for Medium, or M, or Fine, or F, filtermedia).

As described in more detail below, the second layer (e.g., efficiencylayer) may comprise synthetic fibers, amongst other fiber types. In someinstances, the second layer may comprise a relatively high weightpercentage of synthetic fibers (e.g., 100 wt. %). In some embodiments,the second layer may comprise synthetic fibers formed from a meltblownprocess, melt spinning process, centrifugal spinning process, orelectrospinning process. In some instances, the synthetic fibers may becontinuous as described further below. In some embodiments, the secondlayer may comprise synthetic staple fibers. In some embodiments, thesecond layer may comprise relatively little (e.g., less than or equal toabout 10 wt. %, less than or equal to about 5 wt. %, less than or equalto about 3 wt. %, less than or equal to about 1 wt. %) or no glassfibers.

In some embodiments, the second layer (e.g., efficiency layer) may havean average fiber diameter of less than or equal to about 5 microns, lessthan or equal to about 4 microns, less than or equal to about 3 microns,less than or equal to about 2 microns, less than or equal to about 1micron, less than or equal to about 0.9 microns, less than or equal toabout 0.8 microns, less than or equal to about 0.7 microns, less than orequal to about 0.6 microns, less than or equal to about 0.5 microns,less than or equal to about 0.4 microns, less than or equal to about 0.3microns, less than or equal to about 0.2 microns, less than or equal toabout 0.1 microns, less than or equal to about 0.08 microns, or lessthan or equal to about 0.06 microns. In some instances, the averagefiber diameter may be greater than or equal to about 0.05 microns,greater than or equal to about 0.06 microns, greater than or equal toabout 0.07 microns, greater than or equal to about 0.08 microns, greaterthan or equal to about 0.09 microns, greater than or equal to about 0.1micron, greater than or equal to about 0.2 microns, greater than orequal to about 0.3 microns, greater than or equal to about 0.4 microns,greater than or equal to about 0.5 microns, greater than or equal toabout 0.8 microns, greater than or equal to about 1 micron, greater thanor equal to about 2 microns, greater than or equal to about 3 microns,or greater than or equal to about 4 microns. All suitable combinationsof the above-referenced ranges are also possible (e.g., greater than orequal to about 0.05 micron and less than or equal to about 5 microns).

In some embodiments, the fibers in the second layer may have an averagelength which may depend on the method of formation of the fibers. Insome cases, the synthetic fibers may be continuous (e.g., meltblownfibers, spunbond fibers, electrospun fibers, centrifugal spun fibers,etc.). For instance, synthetic fibers may have an average length of atleast about 5 cm, at least about 10 cm, at least about 15 cm, at leastabout 20 cm, at least about 50 cm, at least about 100 cm, at least about200 cm, at least about 500 cm, at least about 700 cm, at least about1000, at least about 1500 cm, at least about 2000 cm, at least about2500 cm, at least about 5000 cm, at least about 10000 cm; and/or lessthan or equal to about 10000 cm, less than or equal to about 5000 cm,less than or equal to about 2500 cm, less than or equal to about 2000cm, less than or equal to about 1000 cm, less than or equal to about 500cm, or less than or equal to about 200 cm. All suitable combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to about 100 cm and less than or equal to about 2500 cm). Othervalues of average fiber length are also possible.

In other embodiments, the synthetic fibers are not continuous (e.g.,staple fibers). In general, synthetic non-continuous fibers may becharacterized as being shorter than continuous synthetic fibers. Forinstance, in some embodiments, the fibers in the second layer may havean average length of greater than or equal to about 0.1 mm, greater thanor equal to about 0.3 mm, greater than or equal to about 0.5 mm, greaterthan or equal to about 0.8 mm, greater than or equal to about 1 mm,greater than or equal to about 3 mm, greater than or equal about 6 mm,greater than or equal about 9 mm, greater than or equal about 12 mm,greater than or equal about 15 mm, greater than or equal about 18 mm,greater than or equal about 20 mm, greater than or equal about 22 mm,greater than or equal about 25 mm, greater than or equal about 28 mm,greater than or equal about 30 mm, greater than or equal about 32 mm,greater than or equal about 35 mm, greater than or equal about 38 mm,greater than or equal about 40 mm, greater than or equal about 42 mm, orgreater than or equal about 45 mm. In some instances, the average lengthof the fibers in the second layer may be less than or equal to about 50mm, less than or equal to about 48 mm, less than or equal to about 45mm, less than or equal to about 42 mm, less than or equal to about 40mm, less than or equal to about 38 mm, less than or equal to about 35mm, less than or equal to about 32 mm, less than or equal to about 30mm, less than or equal to about 27 mm, less than or equal to about 25mm, less than or equal to about 22 mm, less than or equal to about 20mm, less than or equal to about 18 mm, less than or equal to about 15mm, less than or equal to about 12 mm, less than or equal to about 9 mm,less than or equal to about 6 mm, less than or equal to about 3 mm, orless than or equal to about 1 mm. All suitable combinations of theabove-referenced ranges are also possible (e.g., greater than or equalabout 0.1 mm and less than or equal to about 30 mm, greater than orequal about 0.3 mm and less than or equal to about 12 mm).

In some embodiments, in which synthetic fibers are included in thesecond layer, the weight percentage of synthetic fibers in the secondlayer and/or in the weight percentage of synthetic fibers of all fibersin the second layer may be greater than or equal to about 1%, greaterthan or equal to about 20%, greater than or equal to about 40%, greaterthan or equal to about 60%, greater than or equal to about 80%, greaterthan or equal to about 90%, or greater than or equal to about 95%. Insome instances, the weight percentage of synthetic fibers and/or in theweight percentage of synthetic fibers of all fibers in the second layerin the second layer may be less than or equal to about 100%, less thanor equal to about 98%, less than or equal to about 85%, less than orequal to about 75%, less than or equal to about 50%, less than or equalto about 25%, or less than or equal to about 10%. All suitablecombinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 80% and less than or equal to about100%). Other values of weight percentage of synthetic fibers in thesecond layer are also possible. In some embodiments, the second layerincludes 100% synthetic fibers.

In some embodiments, the second layer (e.g., efficiency layer) may havea basis weight of less than or equal to about 120 g/m², less than orequal to about 100 g/m², less than or equal to about 75 g/m², less thanor equal to about 50 g/m², less than or equal to about 35 g/m², lessthan or equal to about 25 g/m², less than or equal to about 20 g/m²,less than or equal to about 15 g/m², less than or equal to about 10g/m², less than or equal to about 5 g/m², less than or equal to about 1g/m², less than or equal to about 0.8 g/m², less than or equal to about0.5 g/m², less than or equal to about 0.1 g/m², less than or equal toabout 0.08 g/m², or less than or equal to about 0.06 g/m². In someinstances, the second layer may have a basis weight of greater than orequal to about 0.05 g/m², greater than or equal to about 0.06 g/m²,greater than or equal to about 0.08 g/m², greater than or equal to about0.1 g/m², greater than or equal to about 0.2 g/m², greater than or equalto about 0.5 g/m², greater than or equal to about 0.8 g/m², greater thanor equal to about 1 g/m², greater than or equal to about 5 g/m², greaterthan or equal to about 10 g/m², greater than or equal to about 15 g/m²,greater than or equal to about 20 g/m², greater than or equal to about30 g/m², greater than or equal to about 40 g/m², greater than or equalto about 50 g/m², greater than or equal to about 60 g/m², greater thanor equal to about 70 g/m², greater than or equal to about 80 g/m²,greater than or equal to about 90 g/m², or greater than or equal toabout 100 g/m². All suitable combinations of the above-referenced rangesare also possible (e.g., greater than or equal to about 0.05 g/m² andless than or equal to about 75 g/m², greater than or equal to about 0.05g/m² and less than or equal to about 120 g/m²). Other values of basisweight are also possible. The basis weight is determined according tothe standard ASTM D-13776.

In some embodiments, the second layer may have a thickness of less thanor equal to about 5 mm, less than or equal to about 4.5 mm, less than orequal to about 4 mm, less than or equal to about 3.5 mm, less than orequal to about 3 mm, less than or equal to about 2.5 mm, less than orequal to about 2 mm, less than or equal to about 1.5 mm, less than orequal to about 1 mm, less than or equal to about 0.5 mm, less than orequal to about 0.1 mm, less than or equal to about 0.05 mm, or less thanor equal to about 0.01 mm. In some instances, the second layer may havea thickness of greater than or equal to about 0.001 mm, greater than orequal to about 0.005 mm, greater than or equal to about 0.01 mm, greaterthan or equal to about 0.05 mm, greater than or equal to about 0.08 mm,greater than or equal to about 0.1 mm, greater than or equal to about0.5 mm, greater than or equal to about 1 mm, greater than or equal toabout 1.5 mm, greater than or equal to about 2 mm, greater than or equalto about 2.5 mm, greater than or equal to about 3 mm, greater than orequal to about 3.5 mm, or greater than or equal to about 4 mm. Allsuitable combinations of the above-referenced ranges are also possible(e.g., greater than or equal to about 0.005 mm and less than or equal toabout 5 mm, greater than or equal to about 0.01 mm and less than orequal to about 1 mm). Other values of average thickness are alsopossible. The thickness may be determined according to the standard ASTMD1777 at 0.3 psi.

In certain embodiments, the second layer (e.g., an efficiency layer) mayinclude a single layer. In other embodiments, however, the second layermay include more than one layer (i.e., sub-layers) to form amulti-layered structure. When a layer includes more than one sub-layer,the plurality of sub-layers may differ based on certain features such asair permeability, basis weight, fiber type, and/or particulateefficiency. In certain cases, the plurality of sub-layers may bediscrete and combined by any suitable method, such as lamination, pointbonding, or collating. In some embodiments, the sub-layers aresubstantially joined to one another (e.g., by lamination, point bonding.thermo-dot bonding, ultrasonic bonding, calendering, use of adhesives(e.g., glue-web), and/or co-pleating). In some cases, sub-layers may beformed as a composite layer (e.g., by a wet laid process).

In some embodiments, the efficiency layer may be electrostaticallycharged. Electrostatic charge may be imparted to the second efficiencylayer or the filter media using methods known to those of ordinary skillin the art including, but not limited to, corona charging, charge bars,hydroentangling charging, triboelectric charging, hydrocharging, or useof additives. In other embodiments, the efficiency layer may not becharged.

A filter media having the filtration layer comprising synthetic fibersdescribed herein may exhibit advantageous and enhanced filtrationperformance characteristics, such as dust holding capacity (DHC) andefficiency.

Filter media described herein may have a relatively high dust holdingcapacity. The dust holding capacity is the difference in the weight ofthe filter media before exposure to a certain amount of fine dust andthe weight of the filter media after the exposure to the fine dust, uponreaching a particular pressure drop across the filter media, divided bythe area of the fiber web. Dust holding capacity may be determinedaccording to the weight (mg) of dust captured per square cm of the media(e.g., through a 100 cm² test area). As determined herein, dust holdingcapacity is measured using aerosol of atomized salt (e.g., KCl)particles using an ASHRAE 52.2 flat sheet test rig tested at 15 fpmvelocity where the final pressure drop when the dust holding capacity ismeasured is 1.5 inches of H₂O on a column. The dust holding capacity maybe determined using the ASHRAE 52.2 standard.

In some embodiments, the filter media may have a dust holding capacityof greater than or equal to about 10 g/m², greater than or equal toabout 20 g/m², greater than or equal to about 25 g/m², greater than orequal to about 50 g/m², greater than or equal to about 75 g/m², greaterthan or equal to about 100 g/m², greater than or equal to about 125g/m², greater than or equal to about 150 g/m², greater than or equal toabout 175 g/m², greater than or equal to about 200 g/m², greater than orequal to about 225 g/m², greater than or equal to about 250 g/m², orgreater than or equal to about 275 g/m². In some instances, the dustholding capacity may be less than or equal to about 300 g/m², less thanor equal to about 275 g/m², less than or equal to about 250 g/m², lessthan or equal to about 225 g/m², less than or equal to about 200 g/m²,less than or equal to about 175 g/m², less than or equal to about 150g/m², less than or equal to about 125 g/m², less than or equal to about100 g/m², less than or equal to about 80 g/m², less than or equal toabout 60 g/m², or less than or equal to about 50 g/m². All suitablecombinations of the above-referenced ranges are possible (e.g., greaterthan or equal to about 10 g/m² and less than or equal to about 300 g/m²,greater than or equal to about 20 g/m² and less than or equal to about80 g/m²).

In some embodiments, the average efficiency of a layer (e.g., secondlayer) and/or filter media increases as a function of particle size. Insome embodiments, the average efficiency may be greater than or equal toabout 20% and less than or equal to about 100% (e.g., greater than orequal to about 40% and less than or equal to about 100%) for 0.3-1.0micron-sized particles, for 1.0-3.0 micron-sized particles, or 3.0-10.0micron-sized particles. For instance, in certain embodiments, theaverage efficiency of a filtration layer (e.g., second layer) and/orfilter media may be greater than or equal to about 10%, greater than orequal to about 20%, greater than or equal to about 35%, greater than orequal to about 50%, greater than or equal to about 60%, greater than orequal to about 70%, greater than or equal to about 80%, greater than orequal to about 90%, greater than or equal to about 95%, greater than orequal to about 97%, greater than or equal to about 99%, greater than orequal to about 99.5%, greater than or equal to about 99.9%, greater thanor equal to about 99.95%, greater than or equal to about 99.99%, orgreater than or equal to about 99.995% for 0.3-1.0 micron-sizedparticles, for 1.0-3.0 micron-sized particles, or 3.0-10.0 micron-sizedparticles. In some embodiments, the average efficiency may be less thanor equal to about 100%, less than or equal to about 99.999%, less thanor equal to about 99.99%, less than or equal to about 99.997%, less thanor equal to about 99.995%, less than or equal to about 99.9%, less thanor equal to about 99.5%, less than or equal to about 99%, less than orequal to about 98%, less than or equal to about 97%, less than or equalto about 95%, less than or equal to about 90%, less than or equal toabout 85%, less than or equal to about 75%, less than or equal to about60%, less than or equal to about 50%, less than or equal to about 40%,less than or equal to about 30%, less than or equal to about 20%, orless than or equal to about 10% for 0.3-1.0 micron-sized particles, for1.0-3.0 micron-sized particles, or 3.0-10.0 micron-sized particles. Itshould be understood that all suitable combinations of theabove-referenced ranges are possible (e.g., greater than or equal toabout 20% and less than or equal to about 100%). The average efficiencyas a function of particle size may be determined according to EN 1822.In some embodiments, the average efficiency of a mechanical efficiencylayer and/or filter media may be tested using EN 1822.

In some embodiments, the average efficiency of the second layer orfilter media may be tested following the ASHRAE 52.2 standard. Forinstance, the average efficiency of a charged efficiency layer and/orfilter media may be tested using ASHRAE 52.2 standard. The testing usesa test air flow rate of 25 FPM. The test is run at an air temperature of69° F., a relative humidity of 25%, and a barometric pressure of 29.30in Hg. The testing also uses a challenge aerosol of atomized salt (e.g.,KCl) particles having a range of particle sizes between 0.3-1.0 microns,1.0-3.0 microns, or 3.0-10.0 microns.

In certain embodiments, the second layer (e.g., efficiency layer) and/orfilter media described herein may be classified by a MERV (MinimumEfficiency Reporting Value) rating based on the results of the ASHRAE52.2 efficiency. MERV ratings are generally used by the HVAC (Heating,Ventilating, and Air Conditioning) industry to describe a filter'sability to remove particulates from the air. A higher MERV rating meansbetter filtration and greater performance. In some embodiments, thesecond layer or filter media described herein has a MERV rating that isin the range of about 5 to 12 (e.g., between about 8 and 12, betweenabout 6 and 9), however the rating can vary based on the intended use.In some embodiments, a filtration layer or filter media described hereinhas a MERV rating of greater than or equal to about 5, greater than orequal to about 6, greater than or equal to about 7, greater than orequal to about 8, greater than or equal to about 9, greater than orequal to about 10, greater than or equal to about 11, or greater than orequal to about 12. The MERV rating may be, for example, less than orequal to 15, less than or equal to 14, less than or equal to 13, lessthan or equal to 12, less than or equal to 11, or less than or equal to10. It should be understood that all suitable combinations of theabove-referenced ranges are possible (e.g., greater than or equal toabout 5 and less than or equal to about 15).

In some embodiments, the air permeability of the filter media may begreater than or equal to about 1 CFM, greater than or equal to about 5CFM, greater than or equal to about 10 CFM, greater than or equal toabout 25 CFM, greater than or equal to about 50 CFM, greater than orequal to about 75 CFM, greater than or equal to about 100 CFM, greaterthan or equal to 125 CFM, greater than or equal to about 150 CFM,greater than or equal to about 175 CFM, greater than or equal to about200 CFM, greater than or equal to 225 CFM, greater than or equal toabout 250 CFM, or greater than or equal to about 275 CFM. In someinstances, the air permeability of the filter media may be less than orequal to about 300 CFM, less than or equal to about 275 CFM, less thanor equal to about 250 CFM, less than or equal to about 225 CFM, lessthan or equal to about 200 CFM, less than or equal to about 175 CFM,less than or equal to about 150 CFM, less than or equal to about 125CFM, less than or equal to about 100 CFM, less than or equal to about 75CFM, less than or equal to about 50 CFM, or less than or equal to about25 CFM. It should be understood that all suitable combinations of theabove-referenced ranges are possible (e.g., greater than or equal toabout 1 CFM and less than or equal to about 300 CFM, greater than orequal to about 10 CFM and less than or equal to about 250 CFM).

In some embodiments, the filter media may have a relatively low pressuredrop. For instance, in some embodiments, the filter media may have apressure drop of less than or equal to about 1,300 Pa, less than orequal to about 1,200 Pa, less than or equal to about 1,000 Pa, less thanor equal to about 750 Pa, less than or equal to about 500 Pa, less thanor equal to about 250 Pa, less than or equal to about 150 Pa, less thanor equal to about 130 Pa, less than or equal to about 100 Pa, less thanor equal to about 80 Pa, less than or equal to about 60 Pa, less than orequal to about 40 Pa, less than or equal to about 20 Pa, or less than orequal to about 10 Pa. In some instances, the filter media may have apressure drop of greater than or equal to about 4 Pa, greater than orequal to about 6 Pa, greater than or equal to about 10 Pa, greater thanor equal to about 20 Pa, greater than or equal to about 40 Pa, greaterthan or equal to about 60 Pa, greater than or equal to about 80 Pa,greater than or equal to about 100 Pa, greater than or equal to about150 Pa, greater than or equal to about 250 Pa, greater than or equal toabout 500 Pa, greater than or equal to about 750 Pa, greater than orequal to about 1,000 Pa, or greater than or equal to about 1,250 Pa. Allsuitable combinations of the above-referenced ranges are also possible(e.g., greater than or equal to about 4 Pa and less than or equal toabout 1,300 Pa, greater than or equal to about 6 Pa and less than orequal to about 130 Pa). The pressure drop, as described herein, can bedetermined at 10.5 FPM face velocity using a TSI 8130 filtration tester,according to ISO 3968.

In some embodiments, the filter media may have a basis weight of greaterthan or equal to about 20 g/m², greater than or equal to about 25 g/m²,greater than or equal to about 50 g/m², greater than or equal to about75 g/m², greater than or equal to about 100 g/m², greater than or equalto about 125 g/m², greater than or equal to about 150 g/m², or greaterthan or equal to about 175 g/m². In some instances, the filter media mayhave a basis weight of less than or equal to about 200 g/m², less thanor equal to about 175 g/m², less than or equal to about 150 g/m², lessthan or equal to about 125 g/m², less than or equal to about 100 g/m²,less than or equal to about 75 g/m², less than or equal to about 50g/m², less than or equal to about 40 g/m², or less than or equal toabout 30 g/m². All suitable combinations of the above-referenced rangesare also possible (e.g., greater than or equal to about 20 g/m² and lessthan or equal to about 200 g/m², greater than or equal to about 25 g/m²and less than or equal to about 125 g/m²). Other values of basis weightare also possible. The basis weight may be determined according to thestandard ASTM D-13776.

In some embodiments, the filter media may have a thickness of greaterthan or equal to about 0.25 mm, greater than or equal to about 0.3 mm,greater than or equal to about 0.4 mm, greater than or equal to about0.5 mm, greater than or equal to about 0.6 mm, greater than or equal toabout 0.8 mm, greater than or equal to about 1.0 mm, greater than orequal to about 1.2 mm, greater than or equal to about 1.5 mm, greaterthan or equal to about 1.8 mm, greater than or equal to about 2.0 mm, orgreater than or equal to about 2.2 mm. In some instances, the filtermedia may have a thickness of less than or equal to about 2.5 mm, lessthan or equal to about 2.2 mm, less than or equal to about 2.0 mm, lessthan or equal to about 1.8 mm, less than or equal to about 1.5 mm, lessthan or equal to about 1.2 mm, less than or equal to about 1.0 mm, lessthan or equal to about 0.8 mm, less than or equal to about 0.6 mm, lessthan or equal to about 0.5 mm, or less than or equal to about 0.4 mm.All suitable combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to about 0.25 mm and less than orequal to about 2.5 mm, greater than or equal to about 0.4 mm and lessthan or equal to about 1.2 mm). The thickness is determined according tothe standard ASTM D1777 at 0.3 psi.

In some embodiments, the filtration layer comprising synthetic fibersmay comprise a relatively high weight percentage of the filter media(e.g., greater than or equal to about 65 wt. %). In certain embodiments,the weight percentage of the filtration layer comprising syntheticfibers in the filter media may be greater than or equal to about 65 wt.%, greater than or equal to about 70 wt. %, greater than or equal toabout 75 wt. %, greater than or equal to about 80 wt. %, greater than orequal to about 85 wt. %, greater than or equal to about 90 wt. %,greater than or equal to about 92 wt. %, greater than or equal to about95 wt. %, greater than or equal to about 97 wt. %, or greater than orequal to about 99 wt. %. In some instances, the weight percentage of thefiltration layer comprising synthetic fibers in the filter media may beless than or equal to about 99.5 wt. %, less than or equal to about 99wt. %, less than or equal to about 98 wt. %, less than or equal to about97 wt. %, less than or equal to about 95 wt. %, less than or equal toabout 92 wt. %, less than or equal to about 90 wt. %, less than or equalto about 85 wt. %, less than or equal to about 80 wt. %, less than orequal to about 75 wt. %, or less than or equal to about 70 wt. %. Allsuitable combinations of the above-referenced ranges are also possible(e.g., greater than or equal to about 65 wt. % and less than or equal toabout 99.5 wt. %, greater than or equal to about 80 wt. % and less thanor equal to about 95 wt. %).

In some embodiments, the filter media may comprise a relatively highweight percentage of coarse diameter fibers. In certain embodiments, thetotal weight percentage of coarse diameter fibers in the filter mediaand/or in the total weight percentage of coarse diameter fibers of allfibers in the filter media may be greater than or equal to about 20 wt.%, greater than or equal to about 30 wt. %, greater than or equal toabout 40 wt. %, greater than or equal to about 50 wt. %, greater than orequal to about 60 wt. %, greater than or equal to about 70 wt. %, orgreater than or equal to about 80 wt. %. In some instances, the totalweight percentage of coarse diameter fibers in the filter media and/orin the total weight percentage of coarse diameter fibers of all fibersin the filter media may be less than or equal to about 85 wt. %, lessthan or equal to about 80 wt. %, less than or equal to about 70 wt. %,less than or equal to about 60 wt. %, less than or equal to about 50 wt.%, less than or equal to about 40 wt. %, less than or equal to about 30wt. %, less than or equal to about 20 wt. %, or less than or equal toabout 15 wt. %. All suitable combinations of the above-referenced rangesare also possible (e.g., greater than or equal to about 20 wt. % andless than or equal to about 85 wt. %, greater than or equal to about 40wt. % and less than or equal to about 70 wt. %).

In certain embodiments, the total weight percentage of fine diameterfibers in the filter media and/or in the total weight percentage of finediameter fibers of all fibers in the filter media may be less than orequal to about 40 wt. %, less than or equal to about 35 wt. %, less thanor equal to about 30 wt. %, less than or equal to about 25 wt. %, lessthan or equal to about 20 wt. %, less than or equal to about 15 wt. %,or less than or equal to about 10 wt. %. In some instances, the totalweight percentage of fine diameter fibers in the filtration layercomprising synthetic fibers and/or in the total weight percentage offine diameter fibers of all fibers in the filter media may be greaterthan or equal to about 5 wt. %, greater than or equal to about 10 wt. %,greater than or equal to about 15 wt. %, greater than or equal to about20 wt. %, greater than or equal to about 25 wt. %, greater than or equalto about 30 wt. %, or greater than or equal to about 35 wt. %. Allsuitable combinations of the above-referenced ranges are also possible(e.g., greater than or equal to about 5 wt. % and less than or equal toabout 40 wt. %, greater than or equal to about 10 wt. % and less than orequal to about 20 wt. %).

In some embodiments, the filter media may contain a relatively highweight percentage of synthetic fibers. For instance, in someembodiments, the weight percentage of synthetic fibers in the filtermedia and/or in the weight percentage of synthetic fibers of all fibersin the filter media may be greater than or equal to about 1%, greaterthan or equal to about 20%, greater than or equal to about 40%, greaterthan or equal to about 60%, greater than or equal to about 80%, greaterthan or equal to about 90%, or greater than or equal to about 95%. Insome instances, the weight percentage of synthetic fibers in the filtermedia and/or in the weight percentage of synthetic fibers of all fibersin the filter media may be less than or equal to about 100%, less thanor equal to about 98%, less than or equal to about 85%, less than orequal to about 75%, less than or equal to about 50%, or less than orequal to about 10%. All suitable combinations of the above-referencedranges are also possible (e.g., greater than or equal to about 80% andless than or equal to about 100%). In some embodiments, the filter mediaincludes 100% synthetic fibers.

In some embodiments, one or more layers (e.g., filtration layercomprising synthetic fibers, second layer) and/or the entire filtermedia is substantially free of glass fibers (e.g., less than 1 wt. %glass fibers, between about 0 wt. % and about 1 wt. % glass fibers). Forinstance, the filtration layer comprising synthetic fibers, secondlayer, and/or the entire filter media may include 0 wt. % glass fibers.

Filter media described herein may be produced using suitable processes,such a wet laid or a non-wet laid process. In some embodiments, thefiltration layer comprising synthetic fibers and/or the filter mediadescribed herein may be produced using a wet laid process. In general, awet laid process involves mixing together of fibers of one or more type;for example, coarse synthetic fibers of one diameter may be mixedtogether with coarse synthetic fibers of another diameter, and/or withfine diameter fibers, to provide a fiber slurry. The slurry may be, forexample, an aqueous-based slurry. In certain embodiments, fibers, areoptionally stored separately, or in combination, in various holdingtanks prior to being mixed together (e.g., to achieve a greater degreeof uniformity in the mixture).

For instance, a first fiber may be mixed and pulped together in onecontainer and a second fiber may be mixed and pulped in a separatecontainer. The first fibers and the second fibers may subsequently becombined together into a single fibrous mixture. Appropriate fibers maybe processed through a pulper before and/or after being mixed together.In some embodiments, combinations of fibers are processed through apulper and/or a holding tank prior to being mixed together. It can beappreciated that other components may also be introduced into themixture. Furthermore, it should be appreciated that other combinationsof fibers types may be used in fiber mixtures, such as the fiber typesdescribed herein.

In certain embodiments, a media including two or more layers, such as afiltration layer comprising synthetic fibers and a second layer isformed by a wet laid process. For example, a first dispersion (e.g., apulp) containing fibers in a solvent (e.g., an aqueous solvent such aswater) can be applied onto a wire conveyor in a papermaking machine(e.g., a fourdrinier or a rotoformer) to form first layer supported bythe wire conveyor. A second dispersion (e.g., another pulp) containingfibers in a solvent (e.g., an aqueous solvent such as water) is appliedonto the first layer either at the same time or subsequent to depositionof the first layer on the wire. Vacuum is continuously applied to thefirst and second dispersions of fibers during the above process toremove the solvent from the fibers, thereby resulting in an articlecontaining first and second layers. The article thus formed is thendried and, if necessary, further processed (e.g., calendered) by usingknown methods to form multi-layered filter media.

Other wet laid processes may also be suitable. Any suitable method forcreating a fiber slurry may be used. In some embodiments, furtheradditives are added to the slurry to facilitate processing. Thetemperature may also be adjusted to a suitable range, for example,between 33° F. and 100° F. (e.g., between 50° F. and 85° F.). In somecases, the temperature of the slurry is maintained. In some instances,the temperature is not actively adjusted.

In some embodiments, the wet laid process uses similar equipment as in aconventional papermaking process, for example, a hydropulper, a formeror a headbox, a dryer, and an optional converter. After appropriatelymixing the slurry in a pulper, the slurry may be pumped into a headboxwhere the slurry may or may not be combined with other slurries. Otheradditives may or may not be added. The slurry may also be diluted withadditional water such that the final concentration of fiber is in asuitable range, such as for example, between about 0.1% and 0.5% byweight.

In some cases, the pH of the fiber slurry may be adjusted as desired.For instance, fibers of the slurry may be dispersed under generallyneutral conditions.

Before the slurry is sent to a headbox, the slurry may optionally bepassed through centrifugal cleaners and/or pressure screens for removingunfiberized material. The slurry may or may not be passed throughadditional equipment such as refiners or deflakers to further enhancethe dispersion of the fibers. For example, deflakers may be useful tosmooth out or remove lumps or protrusions that may arise at any pointduring formation of the fiber slurry. Fibers may then be collected on toa screen or wire at an appropriate rate using any suitable equipment,e.g., a fourdrinier, a rotoformer, a cylinder, or an inclined wirefourdrinier.

In some embodiments, a resin is added to a layer (e.g., a pre-formedlayer formed by a wet-laid process). For instance, as the layer ispassed along an appropriate screen or wire, different componentsincluded in the resin (e.g., polymeric binder and/or other components),which may be in the form of separate emulsions, are added to the fiberlayer using a suitable technique. In some cases, each component of theresin is mixed as an emulsion prior to being combined with the othercomponents and/or layer. The components included in the resin may bepulled through the layer using, for example, gravity and/or vacuum. Insome embodiments, one or more of the components included in the resinmay be diluted with softened water and pumped into the layer. In someembodiments, a resin may be applied to a fiber slurry prior tointroducing the slurry into a headbox. For example, the resin may beintroduced (e.g., injected) into the fiber slurry and impregnated withand/or precipitated on to the fibers. In some embodiments, a resin maybe added to a layer by a solvent saturation process.

In some embodiments, the second layer described herein may be producedusing a non-wet laid process, such as blowing or spinning process. Insome embodiments, the second layer may be formed by an electrospinningprocess. In certain embodiments, the second layer may be formed by ameltblowing system, such as the meltblown system described in U.S.Publication No. 2009/0120048, filed Nov. 7, 2008, and entitled“Meltblown Filter Medium”, and U.S. Publication No. 2012-0152824, filedDec. 17, 2010, and entitled, “Fine Fiber Filter Media and Processes”,each of which is incorporated herein by reference in its entirety forall purposes. In certain embodiments, the second layer may be formed bya meltspinning or a centrifugal spinning process. In some embodiments, anon-wet laid process, such as an air laid or carding process, may beused to form the second layer. For example, in an air laid process,synthetic fibers may be mixed, while air is blown onto a conveyor. In acarding process, in some embodiments, the fibers are manipulated byrollers and extensions (e.g., hooks, needles) associated with therollers. In some cases, forming the layers through a non-wet laidprocess may be more suitable for the production of a highly porousmedia. The layer may be impregnated (e.g., via saturation, spraying,etc.) with any suitable resin, as discussed above. In some embodiments,a non-wet laid process (e.g., meltblown, electrospun) may be used toform the second layer and a wet laid process may be used to form thefiltration layer comprising synthetic fibers. The second layer (e.g.,efficiency layer) and the filtration layer comprising synthetic fibersmay be combined using any suitable process (e.g., adhesives, lamination,co-pleating, or collation).

During or after formation of a filter media, the filter media may befurther processed according to a variety of known techniques. Forinstance, a coating method may be used to include a resin in the filtermedia. Optionally, additional layers can be formed and/or added to afilter media using processes such as adhesives, lamination, co-pleating,or collation. For example, in some cases, two layers (e.g., filtrationlayer comprising synthetic fibers and the second layer) are formed intoa composite article by a wet laid process as described above, and thecomposite article is then combined with a third layer by any suitableprocess (e.g., adhesives, lamination, co-pleating, or collation). It canbe appreciated that a filter media or a composite article formed by theprocesses described herein may be suitably tailored not only based onthe components of each layer, but also according to the effect of usingmultiple layers of varying properties in appropriate combination to formfilter media having the characteristics described herein.

As described herein, in some embodiments two or more layers of thefilter media (e.g., filtration layer comprising synthetic fibers and thesecond layer) may be formed separately and combined by any suitablemethod such as lamination, collation, or by use of adhesives. The two ormore layers may be formed using different processes, or the sameprocess. For example, each of the layers may be independently formed bya non-wet laid process (e.g., meltblown process, melt spinning process,centrifugal spinning process, electrospinning process, dry laid process,air laid process), a wet laid process, or any other suitable process.

Different layers may be adhered together by any suitable method. Forinstance, layers may be adhered by an adhesive and/or melt-bonded to oneanother on either side. Lamination and calendering processes may also beused. In some embodiments, an additional layer may be formed from anytype of fiber or blend of fibers via an added headbox or a coater andappropriately adhered to another layer.

In some embodiments, further processing may involve pleating the filtermedia. For instance, two layers may be joined by a co-pleating process.In some cases, the filter media, or various layers thereof, may besuitably pleated by forming score lines at appropriately spaceddistances apart from one another, allowing the filter media to befolded. In some cases, one layer can be wrapped around a pleated layer.It should be appreciated that any suitable pleating technique may beused.

In some embodiments, a filter media can be post-processed such assubjected to a corrugation process to increase surface area within theweb. In other embodiments, a filter media may be embossed.

The filter media may include any suitable number of layers, e.g., atleast 2, at least 3, at least 4, at least 5, at least 6, at least 7layers. In some embodiments, the filter media may include up to 20layers.

Filter media described herein may be used in an overall filtrationarrangement or filter element. In some embodiments, one or moreadditional layers or components are included with the filter media.Non-limiting examples of additional layers (e.g., a third layer, afourth layer) include a meltblown layer, a wet laid layer, a spunbondlayer, a carded layer, an air-laid layer, a spunlace layer, a forcespunlayer or an electrospun layer.

It should be appreciated that the filter media may include other partsin addition to the one or more layers described herein. In someembodiments, further processing includes incorporation of one or morestructural features and/or stiffening elements. For instance, the filtermedia may be combined with additional structural features such aspolymeric and/or metallic meshes. In one embodiment, a screen backingmay be disposed on the filter media, providing for further Gurleystiffness. In some cases, a screen backing may aid in retaining thepleated configuration. For example, a screen backing may be an expandedmetal wire or an extruded plastic mesh.

In some embodiments, a layer described herein may be a non-woven web. Anon-woven web may include non-oriented fibers (e.g., a randomarrangement of fibers within the web). Examples of non-woven websinclude webs made by wet-laid or non-wet laid processes as describedherein.

The filter media may be incorporated into a variety of suitable filterelements for use in various applications including gas and liquidfiltration. Filter media suitable for gas filtration may be used forHVAC, HEPA, face mask, and ULPA filtration applications. For example,the filter media may be used in heating and air conditioning ducts. Inanother example, the filter media may be used for respirator and facemask applications (e.g., surgical face masks, industrial face masks, andindustrial respirators). The filter media can be incorporated into avariety of filter elements for use in hydraulic filtration applications.Exemplary uses of hydraulic filters (e.g., high-, medium-, andlow-pressure specialty filters) include mobile and industrial filters.

Filter elements may have any suitable configuration as known in the artincluding bag filters and panel filters. Filter assemblies forfiltration applications can include any of a variety of filter mediaand/or filter elements. The filter elements can include theabove-described filter media. Examples of filter elements include gasturbine filter elements, dust collector elements, heavy duty air filterelements, automotive air filter elements, air filter elements for largedisplacement gasoline engines (e.g., SUVs, pickup trucks, trucks), HVACair filter elements, HEPA filter elements, ULPA filter elements, vacuumbag filter elements, fuel filter elements, and oil filter elements(e.g., lube oil filter elements or heavy duty lube oil filter elements).

Filter elements can be incorporated into corresponding filter systems(gas turbine filter systems, heavy duty air filter systems, automotiveair filter systems, HVAC air filter systems, HEPA filter systems, ULPAfilter system, vacuum bag filter systems, fuel filter systems, and oilfilter systems). The filter media can optionally be pleated into any ofa variety of configurations (e.g., panel, cylindrical).

Filter elements can also be in any suitable form, such as radial filterelements, panel filter elements, or channel flow elements. A radialfilter element can include pleated filter media that are constrainedwithin two open wire meshes in a cylindrical shape. During use, fluidscan flow from the outside through the pleated media to the inside of theradial element.

In some cases, the filter element includes a housing that may bedisposed around the filter media. The housing can have variousconfigurations, with the configurations varying based on the intendedapplication. In some embodiments, the housing may be formed of a framethat is disposed around the perimeter of the filter media. For example,the frame may be thermally sealed around the perimeter. In some cases,the frame has a generally rectangular configuration surrounding all foursides of a generally rectangular filter media. The frame may be formedfrom various materials, including for example, cardboard, metal,polymers, or any combination of suitable materials. The filter elementsmay also include a variety of other features known in the art, such asstabilizing features for stabilizing the filter media relative to theframe, spacers, or any other appropriate feature.

As noted above, in some embodiments, the filter media can beincorporated into a bag (or pocket) filter element. A bag filter elementmay be formed by any suitable method, e.g., by placing two filter mediatogether (or folding a single filter media in half), and mating threesides (or two if folded) to one another such that only one side remainsopen, thereby forming a pocket inside the filter. In some embodiments,multiple filter pockets may be attached to a frame to form a filterelement. It should be understood that the filter media and filterelements may have a variety of different constructions and theparticular construction depends on the application in which the filtermedia and elements are used. In some cases, a substrate may be added tothe filter media.

The filter elements may have the same property values as those notedabove in connection with the filter media. For example, the above-notedpressure drop, thicknesses, and/or basis weight may also be found infilter elements.

During use, the filter media mechanically trap contaminant particles onthe filter media as fluid (e.g., air) flows through the filter media.The filter media need not be electrically charged to enhance trapping ofcontamination. Thus, in some embodiments, the filter media are notelectrically charged. However, in some embodiments, the filter media maybe electrically charged. In some embodiments, the filtration layercomprising synthetic fibers (e.g., pleatable backer layer) and/or thefilter media may be used for non-filtration application. For example,the filtration layer comprising synthetic fibers (e.g., pleatable backerlayer) and/or the filter media may be used in window shade applications.

EXAMPLES

This example describes the dust holding capacity for five filter mediaincluding a meltblown efficiency layer adhesively bound to a filtrationlayer comprising synthetic fibers. In this example, the filtration layercomprising synthetic fibers was a pleatable backer layer. The surfaceaverage fiber diameter of the pleatable backer layer varied in eachfilter media. Optimal dust holding capacity was observed when thesurface average fiber diameter (SAFD) was in the range of 13 microns to17 microns.

Filter media containing a metblown efficiency layer and a pleatablebacker layer were formed. The pleatable backer layer was upstream anddirectly adjacent to the meltblown efficiency layer. The efficiencylayer was a meltblown polypropylene fiber web having an average fiberdiameter of 0.6 microns. The efficiency layer was a mechanicalefficiency layer with an F9 efficiency rating according to the EN779standard. The pleatable backer layer contained a blend of a firstpopulation of coarse polyester fibers having an average diameter of 25microns, a second population of coarse polyester fibers having anaverage diameter of 15 microns, a first population of fine polyesterfibers having an average fiber diameter of 9 microns, and a secondpopulation of fine polyester fibers having an average fiber diameter of13 microns, and an acrylic binder. The pleatable backer layers wereformed via a wetlaid process and had a basis weight between about 80g/m² and 85 g/m². Table 1 shows the weight percentage of total fibersfor each fiber type in the pleatable backer layer as well as the surfaceaverage fiber diameter and air permeability. The surface average fiberdiameter was calculated as described herein. Unless otherwise indicated,the structural and performance properties of the layers and entirefilter were measured as described herein.

TABLE 1 Pleatable Backer Layer Properties. Wt. % Wt. % Wt. % 25 15 13Wt. % 9 SAFD Air Perm. Sample microns microns microns microns microns)(CFM) 1 0 7 0 93 8.1 117 2 31.5 7 10.5 51 11.0 202 3 47.2 7 15.8 30 13.5260 4 54.8 7 18.2 20 15.0 352 5 60 7 20 13 16.4 399

Five different pleatable backer layers were combined with the efficiencylayer. The pleatable backer layers differed in the weight percentage offine and coarse diameter fibers that were used and the surface averagefiber diameter. The dust holding capacity was the highest for filtermedia having a surface average fiber diameter of between 13 microns and17 microns. FIG. 2 shows the dust holding capacity versus surfaceaverage fiber diameter for the filter media in Example 1.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Accordingly, the foregoing description and drawings areby way of example only.

What is claimed is:
 1. A filter media, comprising: a non-woven webcomprising: first synthetic fibers having an average fiber diameter ofgreater than or equal to about 15 microns, wherein the weight percentageof first synthetic fibers of all fibers in the non-woven web is greaterthan or equal to about 40 wt. %; and second synthetic fibers having anaverage fiber diameter of greater than or equal to about 0.5 microns andless than about 15 microns, wherein the weight percentage of secondsynthetic fibers of all fibers in the non-woven web is less than orequal to about 50 wt. %, and wherein the surface average fiber diameterof the non-woven web is greater than or equal to about 13 microns andless than or equal to about 17 microns and is measured using theformula:${{SAFD}\left\lbrack {{in}\mspace{14mu} {um}} \right\rbrack} = {4/\left( {{SSA}\mspace{14mu} {\rho \left\lbrack {{in}\frac{g}{{cm}3}} \right\rbrack}} \right)}$wherein SSA is the BET surface of the filtration layer in m²/g and ρ isthe density of the layer in g/cm³; and an efficiency layer, wherein thefilter media has a dust holding capacity of greater than or equal toabout 20 g/m².